This invention relates to a combination weighing method for making various combinations of a plurality of weights of product and selecting therefrom a combination whose sum weight is equal or approximate to a predetermined weight.
Among the prior art combination weighing methods, one method involves utilizing a plurality of weighing units each adapted to weigh a fraction of the weight to be delivered and each adapted for unloading of product therefrom to contribute to a delivery. The method comprises for each delivery the steps of generating the values of combinations of weights on the weighing units which were unloaded in the preceding delivery and comparing the values with an acceptable weight standard to select a combination of weighing units to be unloaded to deliver a sum weight equal or approximate to the aforesaid predetermined weight, unloading the weighing units of the selected combination, loading the weighing units which were unloaded, and wherein, for each delivery, the step of generating and comparing the values of the combinations of weights on the weighing units excluding those units which were unloaded on the preceding delivery is initiated before completion of weighing out new loads in those weighing units. An example of this method is disclosed in coassigned U.S. Pat. Nos. 4,385,671 and 4,470,166.
In another prior art method, a plurality of weighing hoppers, each having a weight sensor, is provided. Each weighing hopper is associated with an auxiliary hopper, and an auxiliary hopper memory is provided corresponding to each auxiliary hopper. Product is weighed by each weighing unit and then transferred to the associated auxiliary hopper memory. The stored values are combined in various fashion to obtain a combination having a weight equal or approximate to a predetermined weight. An example of such method is disclosed in U.S. Pat. No. 4,437,527.
According to a further prior art method, as disclosed in U.S. Pat. No. 4,446,938, a plurality of weighing hoppers, each having an auxiliary hopper, is provided. Product weighed in each weighing hopper is transferred to the auxiliary hopper at the same time as its weight signal is stored in an auxiliary hopper memory. The emptied weighing hopper is reloaded with fresh product, and a combination computation is effected using its weight signal and the content of the auxiliary hopper memory.
According to the above method of '671 patent, it is possible to increase the number of discharges by the weighing units per unit time to obtain high speed operation. However, those weighing units which have been selected for any desired combination cannot participate in another combination computation until their loading, reloading and weighing operations are completed. During this time, therefore, the number of weighing units which can participate in the combination computation or search is reduced, which tends to reduce the accuracy of the selected combination weight. Although this problem can be reduced by increasing the number of weighing units per device, this will undesirably increase the size and cost of the device.
The problem of increase in size is solved by reducing the number of weighing units in accordance with the method of the abovementioned '527 or '938 patent. However, these methods are less effective to increase operational speed, since the unloading and reloading operations are rather time-consuming.